This invention relates to a device for detecting an occurrence of abnormal condition in a load such as a fuel injector for use in an internal combustion engine or the like (hereinafter referred to merely as "a load abnormality detecting device", when applicable).
A conventional load abnormality detecting device will be described with reference to FIG. 1 showing a circuit diagram thereof.
The conventional load abnormality detecting device, as shown in FIG. 1, comprises: a transistor 2 the base of which is connected to a drive unit 1 with an emitter grounded; a load, namely, a fuel injector 3 connected to the collector of the transistor 2; and an abnormality determining circuit 4. The injector 3 is also connected to a 12 V battery.
The operation of the conventional load abnormality detecting device thus organized will be described with reference to FIG. 2 which is a waveform diagram showing a voltage applied to the fuel injector 3.
The battery voltage is applied to the fuel injector 3 through the transistor 2 which is rendered conductive (on) or non-conductive (off) by the drive unit 1. More specifically, as shown in FIG. 2, when the transistor 2 is rendered conductive (on), the 12 V battery voltage is applied to the fuel injector 3, and when the transistor 2 is rendered non-conductive (off) 0 V is applied to the fuel injector 3. That is, a large surge voltage is applied to the fuel injector 3 when the transistor is rendered non-conductive (off).
The abnormality determining circuit 4 determines that the fuel injector 3 is out of order, when no such a surge voltage is applied to the fuel injector 3.
That is, the abnormality is detected from the output waveform of the injector. Hence, it is necessary to provide as many abnormality determining circuits as injectors employed.
As was described above, with the conventional load abnormality detecting device, the abnormality is detected from the output waveform of the injector. Therefore, the conventional load abnormality detecting device suffers from a difficulty that it is necessary to provide one abnormality determining circuit for each of the injectors.
Furthermore, disadvantageously it is difficult for the device to detect the abnormal condition of the fuel injector with high accuracy.